intermittant RPM droppage, engine bucking

[fgross2006]

I still am having an intermittent issue with RMP dropping at red lights, and if I try to accelerate the car continues to pop, pop, pop while raising RPMs.

Yet when it idles right its a dream. I just don't know what causes this and I've tried various things to chase the issue. I first thought I was losing fuel pressure since I was hearing and feeling a bam, bam, bam from the rear when ever this happens and I'm in motion. I upgraded to a Walbro 190 LPH and it didn't change anything.

I swapped out the stock Motorcraft ignition coil with a Accel. I swapped 8.5 mm MSD wires for 9 mm Ford racing wires. I swapped the cap and rotor which had white crust inside with new Motorcraft cap and rotor. A few days ago I had a local muffler shop swap out my X pipe with a stock Mustang H pipe and connect the air system to the rear cats with a brand new stock steel pipe.

Today for the first time in a week, I was at a red light and the RPMs dropped again to an almost stall. I was right at the entrance to the parkway so I got on and brought the car up to 55 mph and there was a definite pop, pop, pop and bucking as I tried to cruise. I could feel like it might stall so I pushed the gas and accelerated for about 10 seconds. I felt pop, pop, pop then it smoothed out and I felt clean acceleration. The care drove great the whole way home. As soon as I got home I immediately threw the code scanner on and took readings. KOEO 11, CM 11, KOER 41.

I expected there to be something in CM since the car had definite problems while running. But the only code coming up is 41 which I know from past experience is a lean condition and a PITA to fix. I don't get it. I dropped a crate motor in last summer, checked and verified TAB TAD setup is working 100% correctly, was getting all 11's on every code scan from last summer till today. Its possible the muffler shop could have left the O2 wire too close to the H pipe and melted the wire. other than that I have no idea what this is or why its happening.

the air tubing that goes to the back of the heads was clogged solid when I pulled it last summer, I cleaned it out before putting it back on the new crate motor. The O2 is grounded to the back of the heads exactly as its supposed to be. I cleaned the paint from that spot and put a thin film of grease to keep it from rusting too fast. And it was a brand new Denso O2 with stock connector, not a universal with a butt connector.

What am I missing or not checking in this situation? I love how the new motor runs when its running right, which is about 98% of the time. But these intermittent fits are ruining the driving enjoyment for me.

[FB71]

Still sounds like fuel pressure. Did you actually measure pressure while the symptom is present? Also, is this a MAF car? An intermittent Maf concern can cause the same symptom, as maf is responsible for fuel delivery calculations.

[fgross2006]

Still sounds like fuel pressure. Did you actually measure pressure while the symptom is present? Also, is this a MAF car? An intermittent Maf concern can cause the same symptom, as maf is responsible for fuel delivery calculations.

my car doesn't have MAF. We checked fuel pressure after installing the Walbro. I cant duplicate the issue when I would be able to get a fuel pressure reading.

[Walking-Tall]

Code 41 in CM = No EGO switch detected-always lean (right)

It's a sensor. The switching happens by the computer varying fuel injected for an above and below "stoich" air:fuel mixture (or whatever AFR it's presently shooting for), so code 41 could mean a number of things in a system like this. It's troubleshootin' time.

This can mean faulty oxygen sensor/circuit/wiring/connections, actual constant lean running (injector, or any of the interrelated system of components/connections that haven't gone south enough to set a trouble code yet), or ignition misfiring (Note: even RICH misfiring sends a boatload of oxygen out the exhaust, which gets FALSELY read (even by a wide band oxygen sensor) as LEAN).

What was/is the fuel pressure at? Whatever it's at is what it'll always be at. It shouldn't be varying, unless the filter's clogging or something, since factory Ford CFI I'm aware of does not vary with a manifold vacuum connection like SEFI does.

[gr79]

O² ground connection to the head.
Grease. Oil.
Insulator, non- conductor.
Silicone dielectric- electrically insulating.
Ok on non conductive surfaces of connector.
Spark plug boots, some other areas ok.

Clean off and use red battery terminal spray.

[FB71]

A dtc 41 isn't the causal code, its the resulting code. An O2 sensor will not cause an intermittent runs rough/bogs/hesitation/backfire. However, any of those conditions will set a 41.

I stand by my opinion that this is a fuel delivery or calculation problem. O2 sensors are not part of fuel calc, they are trim inputs only. Fuel calc is dependent upon load inputs. For a speed/density system, that includes throttle angle, intake air temp, coolant temp, RPM, and barometric pressure. Fuel delivery is dependent upon sufficient flow and pressure of fuel, regulated to the correct pressure. Given this issue is intermittent, I would most likely rule out the fuel pressure regulator. I have seen ruptured regulators cause similar symptoms, but consistently, and always gradually resulting in hydrolock due to ingestion of liquid fuel. I've seen debris in the tank, occasionally blocking the sump, cause the same concern. It was indicated by a drop in pressure during the failure event. The most evil cause I've seen is a clear sandwich baggie stuffed into the fuel tank, floating in the fuel, intermittently blocking the sump. Took me a few hours to find that one.

Proper diagnosis would require the graphing of the above inputs, plus fuel pressure, during the failure event. Any attempt to diagnose or repair without verifying the actual cause is simply guessing, and throwing parts at it.

[FB71]

If you really want to eliminate the O2s from your suspicion, simply unplug them. The car should start and run normally. With them unplugged, the PCM will revert to an FMEM strategy (Failure Mode Effects Manager), and plug in known good values for the O2s. It will set circuit dtcs for the O2s, but now they are not influencing any fuel trim calculations. But again, the O2s aren't involved in fuel delivery/metering calcs anyway.

[FB71]

my car doesn't have MAF. We checked fuel pressure after installing the Walbro. I cant duplicate the issue when I would be able to get a fuel pressure reading.

don't have a portable fuel pressure gauge? Connect to the Schrader valve, route between hood and cowl, pin under a wiper, and go for a drive. Watch pressure during the failure event.

[FB71]

Now that I think about it, I have had a collapsed fuel filter cause a near identical problem...

[xctasy]

Contiuity issues most likelky, IMHO.

I'm sure this is just a check on wires continuity, resistance, and vac lines. As long as the sensors poll within range, the eek!4 will try and get your car running.

As you go up to better exhausts, sometimes the 41 code gets triggered. A guy from the Ford dyno testing division said that the CFI had a poor roosters tail, so somtimes, the CFI triggered a lean condition from the front cylinders, while the back cylinders were getting way too much.

Later 85 CFI's had a different computer with better KAM, a new intake manifold variation, and then, under TSB, a stainless steel eyebrow plate change to bring cylinder to cylinder air fuel mixtures into range. That is what is going on in the background, but the faults are actually simple ones.

I've read through about 50 FEP post stubs for 5.0 HO CFI, including about 4 1984 Tbird EECIII posts because the first eek!4 used a lot of the linear transform EECIII protocols in the newer really fricken smart eek!4 ECU.


I can't find them again quickly, but I think it was zak's post on tracing Code 41. He had a brace of codes (IIRC, 32, 41, 44, 77 or whatever the valid codes were), and then went on a head hunt on systems that generate the fault code. He got it nailed by making sure each wire , vac line and sensor/ solenoid was doing the right thing. He then swapped the orginal computer back in, and it was sweet!

He said that normally, its the secondary air TAB/TAD relays on the strut tower catwalk that cycles the code, and sometimes contacts or vac leaks to the MAP sensor do the rest.


It takes a lot to make the CFI/EECIV system not work. Its the brace of 32/41/44/77 hound bark errors that screw people over. When you get those, you have to go on a time bound Fox hunt, and find the little beasts that trigger the hounds. Like snow tracs in the snow, they don't tell you exactly who tripped the foot prints, but if you use some smarts, you can find out what probably did it.

See http://home.earthlink.net/~jopeterson/Mods.htm

Roller cams? Stock Ford HO roller cams that aren't the aFord aftermarket Deadly letter cams? Entirely Okay!

Ported and really good flowing 3 angle cut GT40 P heads? No

CFI on other wise stock later roller cam engine? Yes.

FEP user Never proved it (it had a 3" pipe, and didn't idle, but that was just a std CFI EECIV brace of fault codes not tuned out ),

http://vb.foureyedpride.com/showthre...98-1985-ltd-lx



He's posted a youtube video, https://www.youtube.com/watch?v=-tu_...ature=youtu.be

I made this for my 85 LTD LX...longtube headers to 2.5" into single 3".





https://youtu.be/-tu_dB1Q7Og

Just a guess but it seemed like too much exhaust for the mild roller 302 that was choked with CFI. Had issues with the car but the engine now has a carb and is going into a Marquis wagon, along with the exhaust.

Straw that breaks the cammels back...?

J Peterson has confirmed it a great exhaust is normally okay as long as the 3 angle valve cut 1995 engine with roller cam isn't sitting under the CFI.



If required for problem cases, good, well resourced Ford Technicians used to real time data load using Thextons 126 Ford EEC-IV Breakout Box used to trace these faults in a real time drive.



Today, people have lost the way; that kind of CPU/ECU technology has fallen away. The old reader was the right way to ensure the Resulting wiring and vac issues are highlighted.

Mean time, Remember, you are seeing only the ghost trail tracks when you pull the codes using your #3145 Code reader.

[Haystack]

Kinda sounds like either poor spark or fuel. Either one would do the exact same thing. I'd go back to the stock coil as well. I've seen quite a few low mileage aftermarket coils fail, while I've never had to replace a stocker.

[xctasy]

JA Cook says the Bloodhound gang idle hunting is possiable even stock...it can get out of range, and the ignition acts as the ISC, taking 6 degrees in and out via the PIP/SPOUT. There is no ISC motor on HO 5.0 CFI's.


I've heard its bad to change the TFI wIring from Fords spec...never, ever go to 9.5 mm wires, keep it stock, and change them if its being laid up on a prolonged basis or used hard. If its a daily driver, the stock Ford spec wires are perfect for use.

Suppression leads aren't something you want to change from stock in TFI, too much hangs on the resistance.

Wires need to avoid cross over, although its less of an issue with TFI and the Cleveland firing order.

Same with the coil spec, and cap and rotor. Fords TFI isn't half the quaity of a good duraspark ii, but its fully electronic, and exactly where Ford wanted to go from the Brown Duraspark III... it does the same job for a significantly reduced cost.



Readthe posts by JA Cook on proper battery grounds...the CFI 5.0 HO is still a really earth sensitive Electronic unit, and zak said pull the hood up a night, turn the light off, and check for electrical crossover. Zak said the wrinig leaves a lot to be desired...every replacement, go up a grade in weight.


Except the plug leads

[fgross2006]

Kinda sounds like either poor spark or fuel. Either one would do the exact same thing. I'd go back to the stock coil as well. I've seen quite a few low mileage aftermarket coils fail, while I've never had to replace a stocker.

I went back to stock coil a year or so back but I kept the brand new accel as a backup. When I started having these issues I swapped the coil to see if it was the source of the problem. The Accell made the car run better, but didn't solve the sputtering at red lights problem. Upgrading the plug wires from MSD 8.5 mm to Ford 9 mm's gave me a performance boost too, but didn't solve the problem.

I have another hunch there might be a kink in my fuel line going to the fuel filter. Im gonna take the car to the muffler shop that did my H pipe swap. They are Mustang guys and I think the mechanic that did the fuel filter move 2 years ago when I did the dual exhaust conversion didn't do it right.

[Supersonic G.T.350]

I'm kinda curious if you've ever checked for a vacuum leak of any kind?

[Jackthemind]

Check for vacuum leaks, make sure the iac isnt sticking, check your timing as well. Do you have an after market fpr?

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